Castanospermine is an alkaloid which has been isolated from the seeds of Castanospermum australe and it has the following formula: ##STR1## Systematically, this compound can be named in several ways as follows: [1S-(1.alpha.,6.beta.,7.alpha.,8a.beta.)]-octahydro-l,6,7,8-indolizinetetr ol or (1S,6S,7R,8R,8aR)-1,6,7,8-tetrahydroxyindolizidine or 1,2,4,8-tetradeoxy-1,4,8-nitrilo-L-glycero-D-galacto-octitol. The term "castanospermine" or the first systematic name will be used in the discussion below.
Esters of castanospermine and their activity as inhibitors of intestinal sucrase and lysosomal glucosidase and their utility in the treatment of diabetes has been described in European Patent Application No. 0 297 534. The indicated patent application describes the preparation of these esters but the procedures involved either give a mixture of esters which must be separated or involve multistep chemical synthesis.